This invention relates to controlled rectifiers and more particularly relates to a novel controlled rectifier having a ring gate which is less subject to dV/dt turn-on.
Controlled rectifiers employing an auxiliary cathode to permit the firing of the device from a very low input gate current are well known. Such devices are shown, for example, in U.S. Pat. No. 3,586,927 in the names of Thomas J. Roach and James H. Hauck and assigned to the assignee of the present invention. Devices employing auxiliary cathodes and main ring gates are also known wherein the main ring gate surrounds and is spaced from a main cathode disc which is in contact with a central diffused emitter region on the upper surface of a semiconductor wafer. The ring gate is disposed atop an auxiliary emitter region and acts as an auxiliary cathode with respect to a small input gate element. The ring gate then acts as the main gate for the main device and causes injection of electrons from the main emitter which in turn fires the device and causes conduction between the main cathode and the anode.
Ring gates are desirable since they increase the rate-of-change-of-current (dI/dt) capability of the device during firing, since the entire emitter area turns on more quickly than in devices in which the main gate is a point gate. However, devices using a ring gate geometry have a high distributed capacitance beyond the main emitter region. Consequently, a voltage having a high dV/dt applied between the cathode and anode can cause sufficient injection of electrons from the emitter through the distributed capacitance to cause dV/dt turn-on of the device.
The principal object of this invention is to retain the desirable dI/dt features of the ring gate structure for a controlled rectifier, but to reduce the sensitivity of the device to firing due to high dV/dt.